Emission control devices, such as diesel particulate filters (DPF), may reduce the amount of soot emissions from a diesel engine by trapping soot particles. Such devices may be regenerated during operation of a turbocharged engine by operating above a regeneration temperature to decrease the amount of trapped particulate matter. An increase in exhaust temperature may be generated in various ways, including a far post injection of fuel that at least partially reacts exothermically in the exhaust system, such as in an oxidation catalyst upstream of the particulate filter. At the same time, the various exhaust components and emission control devices may have upper temperature limits beyond which thermal degradation can occur.
The inventors herein have recognized that in systems such as those noted above, temperature control, particularly of temperatures within the emission control system, may be degraded during transient engine operation. For example, relatively large and rapid change in mass air flow, fuel flow, or other parameters may generate a temporary mismatch in the response of gas flow through the system as compared to fuel flow through the system. Such mismatches can cause temperatures to temporarily rise too high during acceleration, and fall too low during deceleration. Likewise, turbocharger thermal inertial can also affect accurate temperature control, including generating extended drops in temperature during acceleration (due to turbocharger warm-up), and extended increases in temperature during deceleration (due to turbocharger cool-down).
As such, in one approach a method for operating an engine including a DPF is provided. The method includes adjusting a post fuel injection amount based on a rate of change of engine torque during DPF regeneration. As one example, the adjusting includes reducing the amount when the rate of change is positive, and increasing the amount when the rate of change is negative. In this way, it is possible to anticipate the transient over-temperature and/or under-temperature conditions due to the mismatch in transient fueling to transient engine flow, since the rate of change of engine torque correlates to, yet antedates, such effects.
Furthermore, the method may also include delivering exhaust gas to a turbocharger turbine, to an oxidation catalyst, and then a DPF, the adjusting of the post fuel injection further based on thermal inertia of the turbocharger. In this way, it possible to account for the extended temperature differences due to the turbocharger inertia, while still responding to transient changes in engine torque.
As such, regeneration of the DPF may be accurately controlled, while decreasing the likelihood of thermal degradation of the DPF or other emission control devices in the emission control system.
It should be understood that the background and summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.